Year	Number of
1990	6.64
1991	7.14
1992	7.54
1993	8.03
1994	8.38
1995	8.03
1996	7.85
1997	7.73
1998	7.6
1999	7.44
2000	7.31
2001	7.24
2002	7.24
2003	7.45
2004	8.13
2005	8.4
2006	8.69
2007	8.99
2008	9.34
2009	9.77
2010	10
2011	10.21
2012	10.42
2013	10.6
2014	10.79
2015	10.98
2016	10.95